Add async safe() coverage and polish docs/comments

[fprl]

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[Copilot]

Pull request overview

This PR enhances test coverage for the safe() method by adding explicit tests for async function scenarios and improves the clarity of implementation comments.

Key Changes:

• Added test coverage for async functions that reject and resolve in both server and client contexts
• Updated the safe() implementation comment in client.ts to more accurately describe that it accepts both promises and functions

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/errata/test/errata.test.ts	Adds two new tests covering async function rejection and resolution scenarios for the server-side safe() method
packages/errata/test/client.test.ts	Adds two new tests covering async function rejection and resolution scenarios for the client-side safe() method
packages/errata/src/client.ts	Updates the implementation comment to clarify that safe() accepts both promises and functions (replaces "Promise/helper" with "Promise helper or function")

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